The present invention relates to phenolic resin compositions. More particularly, the present invention pertains to a phenolic resin composition which is stable against an environmental moisture change and is excellent in fast curing, flexibility and heat resistance.
A phenolic resin is relatively favorable in curing property, molding property and the like and a cured product thereof is excellent in electrical and mechanical characteristics so that the cured product thereof has widely been utilized for a molding material, a laminated material, a friction material for a disc brake pad and the like, a shell molding material, a casting material, a foamed material and the like as a well-balanced material thereby allowing the cured product thereof to be of an industrially valuable material.
However, the phenolic resin is liable to absorb moisture when an environmental moisture is changed and, once the phenolic resin absorbs the moisture, a curing behavior thereof is changed such that a curing rate is accelerated whereupon, for example, a yield of molded products at the time of molding was deteriorated, qualities of the molded products were varied from one another and the like. However, no effective measure to solve these problems has actually been proposed.
Further, though the phenolic resin can be a binder which has excellent mechanical characteristics, electrical characteristics, heat resistance, adhesivity and the like, the molded product thereof has a drawback that it is inferior in flexibility and vibration absorption. In order to improve these performances, studies on modified phenolic resins have actively been conducted. For example, among others, studies on oil-modified phenol resins, cashew-modified phenol resins, silicone-modified phenolresins, epoxy-modified phenolresins, melamine-modified phenol resins and the like have been conducted whereby some of the above-described modified phenol resins are put in an actual use.
To give one example of such usage, a first Japanese Patent laid-open, namely, Japanese Patent Laid-Open No. 323080/1999, discloses a method of producing a phenol resin composition in which a silicone gel based on an addition reaction type silicone having from 10 to 500 of a penetration number is kneaded into a phenol resin by using a pressure mixer. However, though a modified phenol resin composition obtained by this method has been improved in flexibility, vibration absorption and the like to some extent, stability against the environmental moisture change was insufficient.
Further, a second Japanese Patent laid-open, namely, Japanese Patent Laid-Open No. 071497/1999, discloses a rubber-modified phenol resin composition which is a phenolic resin composition containing a phenol resin which is a polycondensate of a phenol and an aldehyde and has a ratio (o/p ratio) of an ortho-bonding to a para-bonding at a methylene bonding in the resin being from 1.0 to less than 4.5 and a rubber component as essential components, in which acrylonitrile-butadiene rubber (NBR) and an elastomer containing an acrylic acid ester are used as the above-described rubber component.
However, though such a rubber-modified phenolic resin composition as described above has been improved in flexibility, vibration absorption and the like to some extent, heat resistance and stability against the environmental moisture change were insufficient. On this occasion, the o/p ratio described in the above-described Japanese Patent laid-open, namely, the second Japanese Patent laid-open, is determined by a ratio of absorbance of the ortho-bonding appearing in a range of from 730 cmxe2x88x921 to 770 cmxe2x88x921 to that of the para-bonding appearing in a range of from 800 cmxe2x88x921 to 840 cmxe2x88x921 in an infrared absorption spectrum. A value of the o/p ratio obtained by this measuring method comes out lower than that obtained by a measuring method described in embodiments according to the present invention. Specifically, a range of from 1.0 to less than 4.5 of the o/p ratio obtained by this measuring method approximately corresponds to that of from 0.4 to less than 2 of the o/p ratio obtained by the measuring method described in the embodiments according to the present invention.
Furthermore, a third Japanese Patent laid-open, namely, Japanese Patent Laid-Open No. 144106/2000, describes a rubber-modified high-ortho phenolic resin for use as a binder for a non-asbestos-based friction material in which NBR is used as such a rubber component as described above and the ratio (o/p ratio) of the ortho-bonding to the para-bonding at a methylene bonding in a resin portion of the high-ortho phenol resin is 1.0 or more, and, preferably, from 1.0 to 4.5. However, though such a rubber-modified phenolic resin as described above has been improved in flexibility, vibration absorption and the like to some extent, heat resistance and stability against the environmental moisture change were insufficient. On this occasion, the o/p ratio described in this Japanese Patent laid-open, namely, the third Japanese Patent laid-open, is determined by a same measuring method as in Japanese Patent Laid-Open No. 071497/1999, namely, the above-described second Japanese Patent laid-open; therefore, in a same manner as in the second Japanese Patent laid-open, a range of the o/p ratio described in this Japanese Patent laid-open comes out lower than that of the o/p ratio according to the present invention.
In view of the above-described problems, an object of the present invention is to provide a phenolic resin composition which is stable against an environmental moisture change and excellent in fast curing property, flexibility and heat resistance.
Inventors of the present invention have found as a result of an intensive study that, when a resin composition comprising a phenolic resin and a rubber component as essential components is produced, the above-described problems can be solved by using a resin in which a ratio (o/p ratio) of an ortho-bonding to a para-bonding at a methylene bonding in the phenolic resin is controlled to be in a specified range and, further, incorporating a specified quantity of a specified rubber component thereto to achieve the present invention.
In other words, the present invention is a phenolic resin composition, comprising from 70% by weight to 97% by weight of a phenolic resin and from 3% by weight to 30% by weight of a silicone-based rubber component, which is characterized in that a ratio (o/p ratio) of an ortho-bonding to a para-bonding at a methylene bonding in a phenolic resin is from 2 to 9.
As for a preferred aspect of the phenolic resin composition according to the present invention, mentioned is such a resin composition as described above in which a viscosity of a silicone-based rubber is from 5000 mm2/s to 200000 mm2/s at 50xc2x0 C. Further, mentioned is such a phenolic resin composition as described above which is characterized by being a compound of from 85% by weight to 99% by weight of an organopolysiloxane having a silanol group at each terminal of a molecule thereof and from 1% by weight to 15% by weight of a crosslinking agent for silanol condensation as the silicone-based rubber.
As for the organopolysiloxane having a silanol group in each terminal of a molecule thereof, mentioned is a compound which is expressed by the following general formula (1): 
wherein
R1 and R2 are same or different from each other and each individually represents any one of a monovalent hydrocarbon group, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group or the like, an aryl group such as a phenyl group, a xylyl group or the like, and a halogenated monovalent hydrocarbon such as a xcex3-chloropropyl group, a 3,3,3-trifluoropropyl group or the like; and
n represents an integer of from 4 to 675.
Further, as for the crosslinking agent for silanol condensation, mentioned is a multifunctional silane compound in which three or more functional groups of at least one type selected from the group consisting of: an alkoxy group, an acyloxy group, a ketooxime group, an alkenyloxy group, an aminooxy group and an amino group are directly bonded to a silicon atom.
The phenolic resin composition according to the present invention may contain from 3 parts by weight to 20 parts by weight of hexamethylenetetramine based on 100 parts by weight of the resin composition. Such resin composition is advantageously used as a binder for a friction material.
Characteristics of the present invention are present in points of using the phenolic resin in which the ratio (o/p ratio) of the ortho-bonding to the para-bonding at the methylene bonding is controlled to be in the specified range and containing the specified quantity of the silicone-based rubber component. As for the silicone-based rubber component, mentioned is a compound of, preferably, an organopolysiloxane having a silanol group in each terminal of the molecule expressed by the above-described general formula (1) and a crosslinking agent for silanol condensation. On this occasion, the silicone-based rubber having a specified viscosity is preferable.
The phenolic resin composition according to the present invention is stable against the environmental moisture change. Namely, the composition is slow in a hygroscopic rate and small in a gel time change quantity based on a 1%-by-weight moisture absorption. Further, the composition is excellent in fast curing, flexibility and heat resistance. Furthermore, since the composition is excellent in flexibility, when used as a friction material for a brake and the like, the composition is excellent in vibration absorption and brake squeal characteristics. Therefore, the composition is capable of being used for various types of molding materials and friction materials thereby being extremely useful for industrial applications.
On this occasion, the ratio (o/p ratio) of the ortho-bonding to the para-bonding at the methylene bonding in the phenolic resin according to the present invention and the viscosity of the silicone-based rubber are values to be determined by methods described in embodiments which are described on the pages that follow.
The present invention is explained in more detail below.
A phenolic resin composition according to the present invention is produced by adding a rubber component to a phenolic resin and mixing a resultant mixture. The phenolic resin used in the present invention is such a resin as is produced by subjecting a phenol and an aldehyde to polycondensation.
Examples of the phenols for use in producing the phenolic resin include phenol, cresol, xylenol, ethylphenol, propylphenol, catechol, resorcin, hydroquinone, bisphenol-A, bisphenol-F and the like. Among them, phenol is preferable. These phenols may be used individually or in any combination of two or more types thereof.
Examples of aldehydes include formaldehyde, paraformaldehyde, benzaldehyde and the like. These aldehydes may be used individually or in any combination of two or more types thereof. As for a catalyst: to be used at the time of reaction of the phenol and the aldehyde, a metallic salt such as zinc acetate or the like and an acid such as oxalic acid, hydrochloric acid, sulfuric acid, diethyl sulfate, paratoluene sulfonic acid or the like can be used either individually or in any combination of two or more types thereof. Ordinarily, a quantity of the catalyst to be used is from 0.01 part by weight to 5 parts by weight based on 100 parts by weight of the phenol.
As for an effective way to enhance the o/p ratio in the phenolic resin, mentioned is a method in which paraformaldehyde is used as an aldehyde and a catalyst of a divalent metallic salt of manganese, magnesium, zinc or the like is used whereupon a pH of a reaction system is set to be from 4 to 7 and a reaction temperature is controlled to be in a range of from 100xc2x0 C. to 160xc2x0 C.
In the phenolic resin to be used in the present invention, the ratio (o/p ratio) of the ortho-bonding to the para-bonding at the methylene bonding in the resin is from 2 to 9 and, preferably, from 2.5 to 7. When the o/p ratio is less than 2, the curing rate is not sufficiently fast, which generates a difference between curing rates before and after a moisture is absorbed thereby causing a variance in molding property. On this occasion, though depending on situations, a yield at the time of molding can be deteriorated. In this connection, the range of the o/p ratio of from 2 to 9 determined by the method described in the embodiments according to the present invention approximately corresponds to that of from 4.9 to 22 determined by the method by means of an infrared absorption spectrum described in Japanese Patent Laid-Open No. 071497/1999.
For example, when a hygroscopic rate of the phenolic resin composition containing the curing agent is more than 1% by weight/hr under conditions of 25xc2x0 C. and 60% relative humidity (RH), there is a danger that the curing rate may be changed in accordance with the environmental moisture change while the composition is stored. Further, when a gel time change quantity (second at 150xc2x0 C.) of the phenolic resin composition containing the curing agent based on a 1%-by-weight moisture absorption comes to be more than 10 seconds, it is conceivable that the deterioration of a yield of molded products or variance of performances of the molded articles is brought about. Furthermore, when a resin having the o/p ratio of more than 9 is used, at the time of molding, insufficient degassing due to fast curing of a surface of the molded product is likely to cause a bulge therein whereupon molding becomes difficult.
By using a resin having the o/p ratio of from 2 to 9 as the phenolic resin and, also, containing a specified rubber component therein, a molded product which is small in difference between curing rates before and after being affected by the environmental moisture, namely, absorbing the moisture, fast in the curing rate at the time of molding and excellent in flexibility, vibration absorption and heat resistance can be obtained. It is considered that this fact is based on a molecular structure thereof which has become difficult to be affected by the environmental moisture.
The rubber component to be used in the present invention is a silicone-based rubber. As for the silicone-based rubber, a compound of from 85% by weight to 99% by weight of an organopolysiloxane having a silanol group at each terminal of a molecule thereof and from 1% by weight to 15% by weight of a crosslinking agent for silanol condensation is preferable. When the crosslinking agent for silanol condensation is less than 1% by weight, crosslinking of the silicone-based rubber becomes insufficient whereupon improvement effects of flexibility and vibration absorption are impaired; therefore, this case is unfavorable, whereas when the crosslinking agent for silanol condensation is more than 15% by weight, heat resistance is decreased; therefore, this case is also unfavorable.
The above-described favorable silicone-based rubber component is prepared by adding an organopolysiloxane having a silanol group at each terminal of the molecule thereof and a silicone-based emulsifier to a heat-melted phenolic resin and, then, adding the crosslinking agent for silanol condensation and the catalyst for silanol condensation to a resultant mixture to allow a crosslinking reaction to take place in the phenolic resin. As for the organopolysiloxane having the silanol group at each terminal of the molecule thereof, the compound expressed by the above-described general formula (1) is preferable and a number-average molecular weight thereof is preferably from 1000 to 50000.
As for the crosslinking agent for silanol condensation, mentioned is a multifunctional silane compound in which three or more functional groups of at least one type selected from the group consisting of: an alkoxy group, an acyloxy group, a ketooxime group, an alkenyloxy group, an aminooxy group, an amino group and the like are directly bonded to a silicon atom.
Specifically, examples thereof include alkoxysilanes such as methyl trimethoxysilane, vinyl trimethoxysilane, 3-chloropropyl trimethoxysilane, 3-aminopropyl trimethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane, vinyl triethoxysilane, methyl triethoxysilane and the like, ketooximesilanes such as methyl tris(dimethyloxime)silane, methyl tris(methyl ethyl ketooxime)silane and the like, acyloxysilanes such as vinyl triacetoxysilane, methyl triacetoxysilane and the like, alkenyloxysilanes such as vinyl tripropenyloxysilane, methyl triisobutenylsilane and the like, aminooxysilanes such as methyl tris(N,N-diamyl aminooxy)silane and the like and amino silanes such as vinyl tris(N-butyl amino)silane and the like; among them, tetra(n-propoxy) silane and methyl triethoxysilane are preferable. The above-described compounds may be used individually or in any combination of two types or more thereof.
It is preferable that from 2.6 parts by weight to 42.4 parts by weight of the organopolysiloxane having the silanol group at each terminal of the molecule thereof and from 0.03 part by weight to 6.4 parts by weight of the crosslinking agent for silanol condensation are added to 100 parts by weight of the phenolic resin. The crosslinking agents for silanol condensation may be used individually or in any combination of two types or more thereof.
As for the silicone-based emulsifiers, there is no particular limitations and one type or any combination of two types or more of known silicon-based emulsifiers may be used. As for a preferable silicone-based emulsifier, mentioned is a modified silicone oil, having an epoxy group and/or a polyoxyalkylene group at a side chain thereof, which is expressed by the following general formula (2): 
wherein
R1, R2 are same with or different from each other and each individually represents a divalent hydrocarbon of from C2 to C5;
POA represents a polyoxyalkylene group which is an adduct of ethylene oxide and/or propylene oxide;
x represents an integer of from 200 to 990; and
the general formula satisfies that y+z=10xcx9c800 and, at the same time, x+y+z less than 1000.
A molecular weight of the modified silicone oil to be used as this emulsifier, namely, values of x, y and z in the above-described general formula (2) or a chain length of the polyoxyalkylene group is not particularly limited, but there exists a characteristic that, when the value of z (number of polyoxyalkylene group) is increased and, accordingly, the chain length becomes longer, compatibility of the organopolysiloxane having the silanol group at each terminal of the molecule thereof with the phenolic resin is enhanced and, accordingly, a dispersion particle size of the silicone-based rubber contained in the resin becomes minute, whereas, when the value of z is decreased and, accordingly, the chain length becomes shorter, the compatibility is decreased. In other words, by appropriately selecting the values of x, y and z, the particle size of the silicone-based rubber dispersed in the phenolic resin can be controlled to be in a range of from 0.1 xcexcm to 10 xcexcm.
A quantity of the silicone-based emulsifier to be added is not particularly limited, but the quantity is preferably from 0.01 part by weight to 30 parts by weight based on 100 parts by weight of the phenolic resin. When the quantity is less than 0.01 part by weight, it becomes difficult to control the particle size of the silicone-based rubber in the phenolic resin within a range of from 0.1 xcexcm to 10 xcexcm. Further, when the quantity is more than 30 parts by weight, a production cost is increased; this case is unfavorable.
The catalysts for silanol condensation are not particularly limited and one type or a combination of two types or more of known catalysts can be used. Namely, an organic tin compound, an organic zinc compound, an organic cobalt compound and the like which have been used as ever for producing the silicone-based rubber are mentioned, and, among them, the organic tin compound is preferable.
Specifically, mentioned are organic tin compounds such as dibutyltin dilaurate, dibutyltin diacetate, tin oleate, tin naphthenate and the like, and, among them, dibutyltin diacetate is preferable. It is preferable that from 0.1 part by weight to 5 parts by weight of any one of these catalysts for silanol condensation is added to 100 parts by weight of the organopolysiloxane having the silanol group at each terminal of the molecule thereof.
The phenolic resin composition according to the present invention contains from 3% by weight to 30% by weight of the above-described rubber component based on from 70% by weight to 97% by weight of the phenolic resin. When a content of the rubber component is less than 3% by weight, the friction material having flexibility which is one of characteristics of the present invention can not be obtained, whereas, when the content is more than 30% by weight, flowability is decreased to deteriorate an appearance of a molded product or to decrease mechanical strength; this case is unfavorable.
A viscosity of the silicone-based rubber at 50xc2x0 C. is preferably from 5000 mm2/sec to 200000 mm2/sec, and, more preferably, from 10000 mm2/sec to 100000 mm2/sec. When the viscosity thereof is less than 5000 mm2/sec, the silicone-based rubber is separated and deposited on a surface of the resin; this case is unfavorable because there is a danger of giving a detrimental effect to the flowability and the like. Further, when the viscosity thereof is more than 200000 mm2/sec, there exists a drawback that a deterioration of heat resistance is prompted to cause the friction material using the composition to generate brake squeal and the like; this case is also unfavorable.
The phenolic resin composition according to the present invention may concurrently use other rubber components within a scope of not damaging the object of the present invention so long as the above-described ratio of the phenolic resin and the silicone-based rubber is held. Examples of other rubber components which may concurrently be used include NBR, acryl rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), an elastomer containing an acrylic acid ester and the like.
When the phenolic resin composition according to the present invention is used as a molding material, the composition is used by adding a curing agent. Examples of the curing agents include hexamethylenetetramine, various types of epoxy compounds each having two or more functionalities, isocyanates, a trioxane, a cyclic formal and the like. Among them, when curing property, heat resistance and the like are taken into consideration, hexamethylenetetramine is preferable. When hexamethylenetetramine is used as the curing agent, a quantity thereof to be added is from 3 parts by weight to 20 parts by weight and, preferably, from 7 parts by weight to 15 parts by weight based on 100 parts by weight of the phenolic resin composition. When the quantity is less than 3 parts by weight, curing of the resin is insufficient, whereas, when the quantity is more than 20 parts by weight, decomposition gas of hexamethylenetetramine causes a molded product to generate a bulge, a crack and the like therein.
The phenolic resin composition according to the present invention obtained in such a manner as described above is fast curable, excellent in flexibility, vibration absorption and heat resistance and, further, is stable against the environmental moisture change. Specifically, the hygroscopic rate thereof is at most 1% by weight/hr at 25xc2x0 C. and 60% relative humidity (RH).
Examples of applications of the phenolic resin composition according to the present invention include a starting material for a molding material, a binder for organic fibers, a compounding agent for rubber, a binder for a grinding material, a binder for a friction material, a binder for inorganic fibers, a covering agent for an electronic/electric device, a binder for a sliding material, a raw material for an epoxy resin, a curing agent for an epoxy resin and the like. Among them, the binder for the friction material is specifically a favorable application.
The friction material composition is prepared by mixing a base material for molding into the phenolic resin composition containing the above-described curing agent. On this occasion, the phenolic resin composition containing the above-described curing agent is used as a binder for the base material for molding. Examples of such base materials for molding include glass fibers, aramid fibers, carbon fibers, ceramic fibers, calcium carbonate, barium sulfate, molybdenum disulfilde, magnesium oxide, alumina, graphite, organic dusts such as a cashew dust and the like. These are ordinarily used as a mixture of two types or more.
The friction material composition contains from 1% by weight to 33% by weight of the phenolic resin composition containing the curing agent according to the present invention and from 67% by weight to 99% by weight of the above-described base material for molding; preferably, the composition contains from 5% by weight to 23% by weight of the former and from 77% by weight to 95% by weight of the latter. The friction material composition to be obtained by using the phenol resin composition containing the curing agent according to the present invention as a binder provides a friction material which is stable against the environmental moisture change and, further, excellent in fast curing property, flexibility, heat resistance and brake squeal characteristics. For this reason, the friction material composition according to the present invention is extremely useful as a starting material for the friction material for automotive vehicles and the like.